Tolerance rings



W. DIX ETAL TOLERANCE RINGS Oct. 30, 1962 3 Sheets-Sheet 1 OriginalFiled Aug. 8, 1958 TOLERANCE FIELD OF BORE TOLERANCE FIELD Q OF SHAFTSHAFT: I-MAXIMUM DIAMETER,"O" BORE=11I-MAXIMUM DIAMETER,"O"

JI-MINIMUM DlAMETER,"-8" N-MINIMUM DIAMETER,"

FIG.

2 mm Cu RETENTION FORCE H Z'P-P 2 SPRtNG MOVEMENT: f Q

ROTATIONAL MOMENT: M

INVENTORS WILLY DIX SPRING STIFFNESS: c

7 BY GEORG WEHR ATTORNEYS Oct. 30, I962 W. DIX ETAL TOLERANCE RINGS 3Sheets-Sheet 2 i LJ O L! O LI.

RIGID INSTALLATION "P" MAX.

I I u H INST LLATION WITH P I TO ERANCE SLEEVE l I I TOLERANCE FIELOWITH INSTALLATION I {I OF TOLERANCE SLEEVE l j I SPRING MOVEMENTTOLERANCE FIELD INVENTORS FOR RIGID INSTALLATION WILLY DIX y GEORGwEI-IR WWW 'AITQRNEYS Oct. 30, 1962 w. DIX ETAL I 3,061,336

TOLERANCE RINGS Original Filed Aug. 8, 1958 3 Sheets-Sheet 3 FIG. IO

i VENTORS DIX E R6 WEHR ATIORNEYS Unite The present invention relates toa springy tolerance sleeeve or ring for fitting a component of circularperipheral outline in a receiver opening of also circular peripheraloutline with a tight or pressure seating or fit, that is, a fit suchthat the component to be fitted will not turn within the opening.

Tolerance sleeves used for effecting such tight or pressure fit may besubjected either to a static load or a dynamic load. The sleeve issubjected to a static load for instance when a rotational moment is tobe transmitted from the component to the body having the receiveropening and vice-versa; and the sleeve is subjected to a dynamic loadfor instance when it is used to seat the inner and outer cage ring of abearing, respectively, upon the rotary shaft and in the structure inWhich the shaft is mounted or of which it constitutes part.

Theoretically, the problem of seating a shaft or round rod in areceiving opening, which is one frequently encountered in manufacture,is a very simple one. All that is necessary is to co-relate thediameters of the component to be seated and of the opening so that thedesired pressure fit is obtained. However, as is evident, thecorrelation of the diameters requires machining with such closetolerances that this solution is economically not practical in very manyinstances. Accordingly, many attempts have been made to eliminate theneed for very close tolerances by interposing compensating elementsbetween the component to be seated and the receiving opening. None ofthe heretofore known compensating elements including springy tolerancesleeves or rings as now available, have been found fully satisfactory.Again the problem of designing satisfactory tolerance or compensatingelements is theoretically a simple one. However, as will be shown in thesubsequent detailed investigation, various unexpected and diflicultproblems are involved. Among the problems encountered in designingtolerance elements capable of compensating tolerances within aneconomically acceptable range may be mentioned the need for reliableresistance against turning or slipping of the seated component, forsufficient resistance of the springy sleeeve used as tolerance elementto the static or dynamic load to which it may be subjected and forcentering the component to be seated in the opening.

Accordingly, one of the objects of the invention is to provide a noveland improved springy tolerance sleeeve which compensates for variationsin the diameters of the component and the receiving opening within aneconomically satisfactorily wide range.

Another object of the invention is to provide a novel and improvedspringy tolerance sleeve which engages the surfaces to be heldstationary relative to each other with a force of retention high enoughto prevent slipping or turning of the seated component without scoringor marring either of the surfaces.

Still another object of the invention is to provide a novel and improvedspringy tolerance sleeve, the structure of which is such that thesleeeve is capable of absorbing the stationary or dynamic loads forwhich it is designed Without experiencing a permanent deformation thatmay cause a collapse of the sleeve.

A further object of the invention is to provide a novel and improvedspringy tolerance sleeve, the design of States Patent 6 which prevents adeformation of the sleeve such that the axis of the component becomeseccentric relative to the.

center axis of the opening to an unacceptable extent.

Other and further objects, features and adavntages of the invention willbe pointed out hereinafter and set forth in the appended claims formingpart of the application.

The present application is a continuation of application Serial No.753,917, filed August 8, 1958, now abandoned. Application Serial No.753,917 is a continuation-impart of application Serial No. 224,558,filed May 4, 1951, now abandoned.

In the accompanying drawing the problems involved in the design of fullysatisfactory tolerance rings or sleeves are illustrated by means ofcomparative graphs and several preferred embodiments of the applicationare shown by Way of illustration and not by way of limitation.

In the drawing:

FIGURE 1 shows diagrammatically the tolerance fields of a shaft and areceiving opening which must be compensated by a tolerance means.

FIGURE 2 shows diagrammatically the physical magnitudes involved in thefunctioning of a tolerance means in the form of a springy tolerancesleeve or ring.

FIGURE 3 shows diagrammatically the effect of a dynamic load upon aspringy tolerance sleeve.

FIGURE 4 is a comparative graph demonstrating the efiect of a tolerancesleeve according to the invention.

FIGURE 5 is a perspective view of a tolerance sleeve or ring accordingto the invention.

FIGURE 5a is a fragmentary circumferential section of the sleeve.

FIGURE 6 is a fragmentary enlarged plan view upon one sideof thetolerance sleeve according to FIGURE 5.

FIGURE 7 is a plan view upon the opposite side of FIGURE 6.

FIGURE 8 is a section taken on line 88 of FIG- URE 6.

FIGURE 9 is a section taken on line 99 of FIG- URE 7.

FIGURE 10 is a section similar to FIGURE 9 of a modification of thetolerance sleeve.

FIGURE 11 is a sectional view of a bearing seated by means of tolerancesleeves or rings according to the invention, and

FIGURE 12 is a sectional view of the seating of a hand grip by atolerance sleeve or ring according to the invention.

Referring first to FIGURE 1 in detail, this figure shows a shaft orjournal 1 to be seated with a pressure or tight fit in a bore 2 of abody 3.. In FIGURE 1 it is assumed that the diameters of the shaft andthe bore are equal and that said equal diameters arethe maximum alloweddiameters for both the shaft and the bore. It is further assumed thatthe range of tolerances is in the minus range for both the shaft and thebore as is indicated by the hatched areas designated 0 to a. Thefollowing table represents the four possible limit conditions under theabove assumption:

I+III I+IV II-i-III II+IV Shaft 0 0 n -a. Bore 0 a -11.

Slidable Fit- Pressure Fit with Slidable Fit. Fit. Play.

the assumed tolerance range. Theoretically the danger of cracking may becontrolled by adjusting the relative tolerances of the shaft and thebore. But, such adjustment involves complicated machining operations andtimeconsuming setting of the machine tools. As has been pointed outbefore, close tolerances involve costly machining operations and arehence avoided in industry whenever possible.

As also mentioned before, various compensating means have beendeveloped. These compensating means generally involve the insertion ofan elastic element between the shaft and the bore wall. Among the knownelastic elements the most satisfactory ones are springy rings formed ofa corrugated ribbon having corrugations extending across the width ofthe ribbon. The apices only of the corrugations engage the surfaces ofthe shaft and the bore under pressure and the resulting friction retainsthe shaft relative to the bore wall. While tolerance rings of that kindare a step in the right direction, the design of the rings as heretoforeknown does not fully satisfy the afore-outlined conditions as willappear from the subsequent discussion, and it is a basic object of thisinvention to eliminate the shortcomings of the ring or sleeve designs,as heretofore known.

The corrugations of a ring are subjected to a radial compression whenthe ring is forced between the wall of a receiving opening and the wallof the component to be seated. Such compression of the corrugationsproduces a spring force P in each corrugation. This force is the resultof a spring movement ,1 and the spring stiffness c which may beexpressed by the equation:

As is shown in FIGURE 2, at each point of contact of the corrugationapices with the bore wall and the shaft wall respectively, a frictionalforce is produced, the value of which is determined by the spring forceP and the frictional factor a. The sum total of the individual forces offriction (P.y.) represents the force of retention at the joint forcedwhich may be expressed by the equation:

where H,. is the force of retention and z the number of corrugations.

Consequently, the number of z of the corrugations determines the forcewith which the shaft is held stationary in the opening against arotational moment or an axial pull when the spring stiffness c, thespring movement 7'', the friction factor a and the diameter D of theshaft are fixed. The moment of rotation may be expressed by thefollowing equation:

D kg, 2 cm.

where M, is the moment of rotation.

The respective equations are entered in FIGURE 2 and will be evidentfrom the reference letters of the figure.

As has been previously mentioned, it is essential that the tolerancesleeve does not cause scoring or marring of the surfaces between whichit is fitted. To satisfy this condition, the pressure upon a given unitof engaged surface area must be kept within acceptable limits.Accordingly, the number of corrugations upon which the total force ofretention H is distributed must be sufficiently high. The springmovement f which the corrugations permit depends upon the selectedtolerances. As stated before, one of the objects of the invention is toincrease the acceptable range of tolerances above the values heretoforeacceptable in connection with pressure fits. Obviously, largertolerances afford the advantage of reduced manufacturing costs sincethey entail less precision machining. The distance of the springmovement f is obviously materially affected by the used tolerances. Atthe same time, it is essential that the variations in the springmovement f affect the force of retention within such limits only that apressure fit is obtained.

As is evident, changes in the tolerances do not havethe same effect whena spring tolerance ring is used in automatically the variations in thetolerances, to a certain extent. It is further evident that the effectof variations in the tolerances is the less marked the softer the springaction of the ring is. These facts would seem to suggest theadvisability of rings having a low spring stiff ness 0, that is, ringshaving shallow corrugations and a relatively wide spacing of thecorrugations. However, the use of comparatively soft tolerance rings isnot a practical solution of the problem. One of the basic requirementsin seating any circular component in a receiving opening, such as of ashaft in a bore, is that the center axes of the shaft or other componentand the bore coincide. When the springiness of the corrugations is low,the displacement of the axis of the shaft to the axis of the borebecomes high. Hence, such displacements are not acceptable therequirement for the coincidence of the center axis calls for a highspringiness of the corrugations, that is, rings, the corrugation ofwhich having small spacings and high amplitudes. Accordingly, there aretwo contradictory aspects to be satisfied. However as the heretoforeknown rings do not take account of these contradictory aspects, it isnow apparent, the use of conventional tolerance rings formed bycorrugated ribbons, that is, ribbons the corrugations of which extendacross the entire width of the ribbon does not afford a marked advantageover a rigid installation, that is, an installation without theinterposition of an elastic tolerance element.

The previous observations were concerned with pressure fits subjected toa static load as exerted by a moment of rotation or an axial pull. Theconditions are even more unfavorable when conventional tolerance ringsin the form of corrugated ribbons are subjected to a dynamic load. As isevident, the circumferential distance between apices of each twoadjacent corrugations will be changed due to the radial compressionexperienced by the corrugation directly opposite the load. Such changesresult automatically in a reduction of the stiffness of the springmaterial directly opposite the load which has the cumulative effect thatthe action of the load becomes still stronger thereby causing finally adestruction of the tolerance ring. For that reason, it is practicallyimpossible to use springy tolerance rings or sleeves as heretofore knownfor the installation of roller bearings. In such installations, thetolerance rings must absorb the load to which the bearing is subjected,in addition to compensating for the manufacturing tolerances. Tests haveshown that the rings are rapidly and permanently pressed out of shapedue to the continuous changes in the load upon the bearings. As aresult, the rings lose very soon their initial springiness and, hence,cannot prevent a loosening of the bearing rings.

FIGURE 3 shows a shaft 5 which should be visualized as being journalledin an inner bearing ring 6 only diagrammatically indicated. A tolerancering 7 is interposed between the bearing ring and the shaft. The load ispresumed to be downward as indicated by a heavy arrow 8. As a result thehighest load, indicated by arrow 9 must be taken up by the corrugation7' whereas the loads to be taken up by the corrugations on both sides ofcorrugation 7 become successively smaller as indicated by the vectordiagrams. The load 9 tends to flatten corrugation 7' thereby causingthat corrugation to spread laterally. The lateral spreading force is notopposed by an equal force in opposite direction, due to the lower loadsacting upon the adjacent corrugations. This effect is cumulative as eachsuccessive corrugation, as seen from load 9, takes up less load. Theresulting strong and repeated deformation of the corrugations results ina rapid and permanent deformation causing a loss of springiness and afinal destruction of the tolerance ring, or at least of its effectiveness.

As appears from the previous analysis, it is inherent in the structureof corrugations extending across the entire width of the tolerance ring,that low corrugation amplitude is combined with high spring stiffnessand vice-versa, that :high corrugation amplitude is combined with lowSpring stiffness. It is further apparent from the previous analysis thatrings having such basic characteristics are inherently incapable ofperforming satisfactorily. The inventors herein have conceived that onlyrings or sleeves can satisfy the aforementioned requirements, thecorrugation of which cannot spread laterally by the pressure of a loadand have a high springiness at the beginning of the compression and alow sprininess when further compressed. In a satisfactory ring therelation between the spring movement of the corrugations and the forcerequired to cause such movement should be approximately as is shown inFIGURE 4. This figure also shows, by way of comparison, the conditionsfor a rigid installation, that is, without the interposition of aspringy tolerance ring. In a rigid installation, the spring force Pincreases rapidly along a very steep linear line. Accordingly, theacceptable tolerance field as defined by P minimum and P maximum is avery narrow one; hence precision machining is required. Incontradistinction thereto, in an installation employing a tolerance ringaccording to the invention, that is, a ring having a low corrugationamplitude and a low spring stiffness, the spring force P increases firstcomparatively rapidly, then the increase becomes rather shallow, andfinally there is a marked drop in the force P when the spring capacityof the corrugations is exhausted and the spring material begins toundergo a permanent deformation. When the load increases over the valuenecessary to establish the retention forces, that is, the amount ofcompression of the corrugations reaches a certain limit, thesprin-giness of the corrugations changes radically, as the closed endsof the corrugations will participate less in carrying the load after acertain deformation has been reached.

FIGURE 4 shows in a second graph the relation of the force P to thespring movement 1 of a tolerance ring according to the invention. As canbe readily seen, the tolerance field is of a width such that allpractically used tolerances can be bridged. When the bore has itsmaximum diameter and the shaft its minimum diameter, the corrugations ofthe ring will be compressed already to such an extent that the force Pminimum required for the pressure fit is produced. As a result, theforce P can then vary only between the comparatively narrow limits of Pminimum and P maximum within the possible tolerance field to -a asdefined in FIGURE 1.

According to the invention, the corrugations of conventional rings orsleeves which extend across the entire width of the ring are replaced bytransverse corrugations which terminate short of each circumferentialedge of the ring and smooth marginal strips are provided along eachtransverse end of the corrugations. The corrugations themselves arepreferably of sine-shaped cross section and the ends of the corrugationsare each faired into the smooth marginal strips by a smoothly roundedend portion preferably forming approximately segments of an ellipsoid orsphere.

The specific configuration of the tolerance rings or sleeves accordingto the invention will now be described in connection with FIGURES 5through 10. As is shown in these figures, the tolerance ring or sleevegenerally designated by is made of a metal ribbon of suitable springymetal and suitable gauge, generally a gauge of 0.2. to 0.8 mm. The ringhas a circumferential middle portion and two circumferential outerportions. The middle portion is corrugated along its entirecircumference to form corrugations 11 whereas the outer portions 12 and13 are smooth strips. Both ends of each corrugation are closed by beingfaired into the respective smooth strip 12 or 13 by a rounded endportion 11'. The corrugations when cut along a circumferential linedefine a sine-line as can best be seen in FIGURE 8. Each end portion 11'joins the rounded apex portion of the respective corrugation to therespective smooth outer strip so as to form a smoother roundedconfiguration gradually flattening out into the flat marginal strip. Therounding of each edge portion constitutes approximately a segment of anellipsoidal geometrical configuration.

The ring is preferably transversely split and the adjacent ends are bentinwardly to form butt portions 14 as shown in FIGURE 5a.

In FIGURES 6, 7 and 9 one of the marginal strips is disposed coplanar oraligned with the plane of the apices on one side of the ring and theother is disposed coplanar or aligned with the apices on the other sideof the ring. However, as shown in FIGURE 10, the marginal smooth strips12 and 13 may also be disposed in a circumferential plane intermediateof the apices of the corrugations.

As is evident, corrugations closed at both ends by smoothly rounded endportions and smooth strips extend ing along the corrugations, haveinherently a much higher stiffness than the conventional opencorrugations, that is, corrugations which extend to the circumferentialedges of the ribbon. Furthermore, the marginal strips, being notstretchable, also fix the circumferential distance t between the apicesof each two adjacent corrugations.

As a result, the corrugations cannot be readily flattened by a staticload or even by a dynamic load such as has been explained in connectionwith FIGURE 3 and the circumference of the ring cannot be appreciablyexpanded by the pressure of a load. In other words, corrugationsaccording to the invention show approximately the desirable attitude ofthe respective graph of FIGURE 4.

The specific dimensions of a tolerance ring or sleeve according to theinvention can be readily calculated as has been previously explained.The equations for calculating the tolerance ring pro-suppose that thespring stiffness is known. It has been found that the spring stiffnessof a tolerance ring or sleeve according to the invention can becalculated with sufiicient accuracy for the part of the graph accordingto FIGURE 4 which is the one important in practice from the ratio ofthickness of the ring material to the spacing t of the apices cubed andmultiplied with the module E of elasticity of the material, the width ofthe ring and an empirically determined correction factor. Accordingly,the calculation of the spring stiffness 0 may be expressed by theequation:

FIGURE 11 shows an arrangement in which the cages of ball bearings aremounted by means of tolerance rings according to the invention. There isshown a hub-shaped machine part 15 in which a rotary shaft 16 isjournalled by means of two ball bearings. Each bearing comprises anouter cage ring 17 and an inner cage ring 18 between which the balls 19of the bearing can rotate. The hub 15 has two radial bores 20' whichform seating surfaces for the outer cages 17. The diameters of thesebores are presumed to be formed with economically acceptable tolerances.The outer cages 17 are pressed into bores 20 each together withtolerance ring 10. The dimensions of the tolerance rings as to the gaugeof the ring material, the spacing t of the corrugations and theamplitude 11 are selected in accordance with the desired fittingpressure. Similarly, the inner cages 18 are fitted upon the seatingsurface 21 of shaft 16 by interposing suitably dimensioned tolerancerings 10. The seating surface of the shaft and the diameter of the shaftat said seating surface can be manufactured with the usual comparativelywide tolerances so that the machining of the surfaces involved does notoffer any difficulties. The tolerance rings according to the inventionafford the additional advantage that the diameter of the shaft at theseating surface may be the same as the general diameter of the shaft.Hence, it is not necessary to provide special seating surfaces having alarger diameter than that of the shaft.

1e om.

The provision and use of tolerance rings according to the invention forthe fitting and mounting of bearings such as ball bearings, rollerbearings or needle bearings, have also the advantage that it is notnecessary to provide play for the bearing since any deformation of thecages of the bearings is avoided or absorbed by the springiness of thetolerance rings. Furthermore, the invention permits the seating ofmachine parts made of different metals within each other sincecoefiicients of expansion of the parts are readily compensated by thespringiness of the tolerance rings.

The tolerance rings or sleeves according to the invention also lendthemselves readily for fitting a part such as a rod or bar in the boreof another part made of plastic. Heretofore, plastic parts such as gripsor knobs had to be secured to bars, rods or lever practicallyexclusively by thread connections. It is virtually impossible, at leaston an economic basis, to provide in a plastic part bores with dimensionsaccurate enough for a pressure fit. Furthermore, even the slightestdeviations in the dimensions of a bore in a plastic part may result in acracking thereof when the rod or other part is forced into the plasticpart. FIGURE 12 shows the seating of a bar 25 in the bore 26 of aplastic knob 27. Bar 25 is frictionally secured in the bore by theinterposition of a tolerance ring 10. As is evident, the load to whichthe tolerance ring is subjected is a static load. Obviously any othercomponents subjected to a static load can be similarly joined with apressure fit by tolerance rings according to the invention.

While the invention has been described in detail with respect to certainnow preferred examples and embodiments of the invention, it will beunderstood by those skilled in the art after understanding theinvention, that various changes and modifications may be made withoutdeparting from the spirit and scope of the invention, and it isintended, therefore, to cover all such changes and modifications in theappended claims.

We claim:

1. In a bearing, a tolerance ring for frictional engagement with each ofa pair of radially spaced annular surfaces, said ring being formed ofspringy sheet metal as a generally cylindrical split sleeve, theimprovements of a plurality of individual corrugations of substantialaxial and radial extent formed in only the center portion of thecircumferential surface of said ring and cooperatively defining anoverall sinusoidal configuration, the curved radial extremities only ofeach of said corrugations being adapted to contact both of said annularsurfaces in line contact therewith, the generally annular axialextremities of said ring lying outside the confines of saidcorrugations, respectively, and being of substantially constant radiusat least as great as the radius of the inner annular surface and nogreater than the radius of the outer of said annular surfaces, thecorrugations having radially and axially tapered terminal portionsblending smoothly into said axial extremities.

2. In a bearing, a tolerance ring as defined in claim 1, the furtherimprovement of said axial extremities being in full circumferentialcontact with an inner one of said radially spaced surfaces and thecorrugations lying radially outside the annular axial extremities tocontact an outer one of said radially spaced surfaces.

3. In a bearing, a tolerance ring as defined in claim 1, the furtherimprovement of said axial extremities being in full circumferentialcontact with an outer one of said radially spaced surfaces and thecorrugations lying radially inside the annular axial extremities tocontact an inner one of said radially spaced surfaces.

4. In a bearing, a tolerance ring for frictional engagement with each ofa pair of radially spaced annular surfaces, said ring being formed ofspringy sheet metal as a generally cylindrical split sleeve, theimprovements of a plurality of individual axially extending corrugationsof substantial axial extent and radial depth embossed in theintermediate portions of the circumferential surface of said ring toform directly opposing concave and convex areas throughout the entireperiphery of the ring, cooperatively defining an overall sinusoidalconfiguration, the curved radial extremities only of each of said saidcorrugations being adapted to contact both of said annular surfaces inline contact therewith, the generally annular axial extremities of saidring being smooth and lying axially outside the confines of saidcorrugations, respectively, and being of substantially constant radiusat least as great as the radius of the inner annular surface and nogreater than the radius of the outer annular surface, the corrugationshaving axially tapered segmental ellipsoidal terminal portions blendingsmoothly into said axial =extremities.

References Cited in the file of this patent UNITED STATES PATENTS1,290,180 Halbleib Jan. 7, 1919 1,384,173 Wikander July 12, 19212,931,412 Wing Apr. 5, 1960 UNITED STATES PATENT OFFICE CERTIFICATE OFCORRECTION Patent N00 $061,386 October 30 1962 Willy Dix et 310 It ishereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 3 line 40., for "forced"- read formed column 5 line 12, for"'sprininess" read springiness Signed and sealed this 4th day of June1963o (SEAL) Attest:

ERNEST w. SWIDER DAVID LADD Attesting Officer I Commissioner of Patents

